This invention relates to a warning apparatus for a vehicle such as an automobile which can warn the operator of the vehicle when there is the possibility of a collision with an obstacle located in front of the vehicle. More particularly, it relates to a warning apparatus which varies the conditions which must be satisfied for a warning to be generated in accordance with the physical or mental state of the driver, the driving characteristics or the driver, environmental conditions, or other factors.
Various collision warning devices for passenger vehicles have been proposed in the past. In these devices, some form of radiation, such as a laser beam or radar, is used to determine the separation between a vehicle in which the warning device is installed and an obstacle located in front of the vehicle, such as another vehicle or a pedestrian. Based on the speed of the vehicle and the rate of change of the distance between the vehicle and the obstacle, the warning device determines when there is danger of a collision between the vehicle and the obstacle and generates a warning to alert the driver to take evasive action.
In a conventional warning device, a warning is generated whenever prescribed conditions are satisfied. However, the reaction time of the driver of a vehicle and the ability of the vehicle to stop in order to avoid an accident vary greatly in accordance with the circumstances. For example, when the driver is tired, he takes longer to react to a warning than when he is alert. Similarly, it takes much longer for a vehicle to stop on a wet road surface than on a dry one. If the conditions to be satisfied in order for the warning to be generated are chosen conservatively so as to allow the driver ample time to stop the vehicle even when the driver is tired or when the road conditions are bad, the warning will be generated even in situations when unnecessary and will become an annoyance to the driver. On the other hand, if the conditions to be satisfied are chosen with a smaller margin of safety so that the warning will be generated in fewer situations, there may be situations in which the warning does not leave the driver sufficient time to safely stop the vehicle and avoid an accident.